1. Field of the Invention
This invention relates to surface controlled subsurface safety valves for use in wells having a tubing string disposed within a casing string.
2. Description of the Prior Art
Surface controlled subsurface safety valves utilized in well installations are well known. Such valves are normally biased towards a closed position and held open by hydraulic fluid pressure or control pressure from the well surface. The hydraulic or control fluid may either be liquid or gas.
A typical valve is shown in U.S. Pat. No. 4,086,935 to George M. Raulins, et al, in which control pressure acts on a sliding seal or piston to overcome a spring and open the valve closure means. The valve is made up as part of the production tubing string having a common longitudinal bore. Thus, opening and closing the valve closure means controls fluid flow through the production tubing string.
Many wells have a casing string with a production tubing string disposed therein. Sometimes it is desirable to produce formation fluids through both the tubing and the annulus between the tubing and casing. U.S. Pat. No. 4,049,052 discloses an annulus safety valve to control flow in the annulus between tubing and casing and may include a tubing safety valve to control flow within the tubing.
U.S. Pat. No. 3,375,874 to V. R. Cherry, et al, discloses a subsurace safety valve particularly adapted for use in gas storage wells. The safety valve disclosed in U.S. Pat. No. 3,375,874 requires a special conduit to direct control fluid from the well surface to the safety valve. The valve actuating means within the safety valve is not wireline retrievable. Both the tubing and the safety valve must be withdrawn from the well to repair a damaged seal within the actuating means shown in U.S. Pat. No. 3,375,874.
The present invention is shown as a safety valve particularly adapted for use in gas storage wells with gas used as the control fluid. The present invention can be easily modified for use in any oil or gas well with either gas or liquid as the control fluid.